I have a LSS 1 x 12 combo with the 1x 12 ext cab and I have a LSC head that I run with a Dr Z 2 x 12 Z best cab. Here are some observations:
1. The base tone of the two amps is easily distinguishable at any "loud" volumes. The LSS is "lighter", its "whispier", its "more jangly"; its more trebly but without being brittle; its "airier". The LSC is all Fender- darker, warmer, "honkier", BIGGER. Listen to the Buddy Whittington clips on the Dr Z website- thats what the LSS sounds like and I think its easily distinguishable from the typical Fender 6L6 tone that the LSC produces.
2. Someone said something about Class A amps and single coils being magic and I think there is a lot of truth to that (both with the LSS and a Dr. Z Maz 38 that I run with the Z 2 x 12). The other side of that is that I have a hard time with those amps and humbuckers- other than at HUGE volumes. Once I ran my PRS Cu 24 with the LSS run into the Z best cab and at headache volumes, it was nothing short of amazing. But short of big volume, the EL-84 Class A amps sure seem better with single coils.
3. The additional 1 x 12 cab with the LSS does give it more perceived clean headroom, but I can only imagine that being a problem at big volume.
4. The 5 watt setting on the LSS produces what I think is the best clean I can get (over the Z, the LSC, a Vibro King, and A Victoria). The airier whispiness makes it just perfect- and loud enough.
5. One other thing- I'm just about done running amps with only one speaker. IMHO, the extra speaker(s) just adds a bigness, an openess, and a crisper bass response across all amps I own. You get around the weight issues with either 1x 12 combos (with an ext cab) or heads with cabs.
6. I've suggested this before, but the amp Mesa should make is one that will reproduce the LSC and LSS tones in one amp (by using the tube assignability like the RK). 4 channels (two LSC, two LSS). I'd buy that amp sight unseen.